feat(apple): native SwiftUI app for iOS and macOS

Add a native SwiftUI VniDrop app (Send/Receive/Settings) talking to the
Rust core via generated UniFFI Swift bindings, plus the uniffi-bindgen
helper crate. iOS uses a TabView, macOS a NavigationSplitView sidebar.

apple/VniDrop/Resources/Assets.xcassets/AppIcon.appiconset/Contents.json

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+{
+  "images" : [
+    { "idiom" : "universal", "platform" : "ios", "size" : "1024x1024", "filename" : "app-icon.png" },
+    { "idiom" : "mac", "scale" : "2x", "size" : "512x512", "filename" : "app-icon.png" }
+  ],
+  "info" : { "author" : "xcode", "version" : 1 }
+}

apple/VniDrop/Resources/Assets.xcassets/Contents.json

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+{ "info" : { "author" : "xcode", "version" : 1 } }

apple/VniDrop/Resources/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>$(DEVELOPMENT_LANGUAGE)</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>$(MARKETING_VERSION)</string>
+	<key>CFBundleVersion</key>
+	<string>$(CURRENT_PROJECT_VERSION)</string>
+	<key>CADisableMinimumFrameDurationOnPhone</key>
+	<true/>
+	<key>UILaunchScreen</key>
+	<dict/>
+	<key>CFBundleDocumentTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleTypeName</key>
+			<string>VniDrop Invitation</string>
+			<key>CFBundleTypeRole</key>
+			<string>Viewer</string>
+			<key>LSHandlerRank</key>
+			<string>Owner</string>
+			<key>LSItemContentTypes</key>
+			<array>
+				<string>com.vnidrop.app.invitation</string>
+			</array>
+		</dict>
+	</array>
+	<key>UTExportedTypeDeclarations</key>
+	<array>
+		<dict>
+			<key>UTTypeConformsTo</key>
+			<array>
+				<string>public.data</string>
+			</array>
+			<key>UTTypeDescription</key>
+			<string>VniDrop Invitation</string>
+			<key>UTTypeIdentifier</key>
+			<string>com.vnidrop.app.invitation</string>
+			<key>UTTypeTagSpecification</key>
+			<dict>
+				<key>public.filename-extension</key>
+				<array>
+					<string>vnd</string>
+				</array>
+				<key>public.mime-type</key>
+				<string>application/vnd.vnidrop.transfer</string>
+			</dict>
+		</dict>
+	</array>
+	<key>LSSupportsOpeningDocumentsInPlace</key>
+	<true/>
+	<key>UIFileSharingEnabled</key>
+	<true/>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>fetch</string>
+		<string>processing</string>
+		<string>remote-notification</string>
+	</array>
+	<key>UIViewControllerBasedStatusBarAppearance</key>
+	<true/>
+	<key>NSCameraUsageDescription</key>
+	<string>VniDrop uses the camera to scan transfer QR codes.</string>
+	<key>NFCReaderUsageDescription</key>
+	<string>VniDrop uses NFC to read transfer invitation tags.</string>
+	<key>NSLocalNetworkUsageDescription</key>
+	<string>VniDrop needs local network access to send to other local devices if needed.</string>
+	<key>NSBonjourServices</key>
+	<array>
+		<string></string>
+	</array>
+</dict>
+</plist>

apple/VniDrop/Resources/VniDrop.entitlements

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<!-- iOS: NFC NDEF reading (matches the original iosApp entitlements). -->
+	<key>com.apple.developer.nfc.readersession.formats</key>
+	<array>
+		<string>NDEF</string>
+	</array>
+
+	<!-- macOS App Sandbox: user-selected files for share/receive, and network
+	     client/server for the local P2P transfer. These keys are ignored on iOS. -->
+	<key>com.apple.security.app-sandbox</key>
+	<true/>
+	<key>com.apple.security.files.user-selected.read-write</key>
+	<true/>
+	<key>com.apple.security.files.downloads.read-write</key>
+	<true/>
+	<key>com.apple.security.network.client</key>
+	<true/>
+	<key>com.apple.security.network.server</key>
+	<true/>
+</dict>
+</plist>